add Command pattern

Author: JakubVojvoda

command/Command.py

@@ -0,0 +1,63 @@
+#
+# Python Design Patterns: Command
+# Author: Jakub Vojvoda [github.com/JakubVojvoda]
+# 2016
+#
+# Source code is licensed under MIT License
+# (for more details see LICENSE)
+# 
+
+import sys
+
+#
+# Receiver
+# knows how to perform the operations associated 
+# with carrying out a request
+#
+class Receiver:
+  def action(self):
+    print("Receiver: execute action.")
+
+#
+# Command
+# declares an interface for all commands
+#
+class Command:
+  def execute(self):
+    pass
+
+#
+# Concrete Command
+# implements execute by invoking the corresponding 
+# operation(s) on Receiver 
+#
+class ConcreteCommand(Command):
+  def __init__(self, receiver):
+    self._receiver = receiver
+
+  def execute(self):
+    self._receiver.action()
+
+#
+# Invoker
+# asks the command to carry out the request
+#
+class Invoker:
+  def __init__(self):
+    self._command = None  
+  
+  def set(self, command):
+    self._command = command
+
+  def confirm(self):
+    if (self._command is not None):
+      self._command.execute()
+
+
+if __name__ == "__main__":
+  receiver = Receiver()
+  command = ConcreteCommand(receiver)
+
+  invoker = Invoker()
+  invoker.set(command)
+  invoker.confirm()